The present invention relates to a hush mode disabling circuit for a self contained smoke alarm that is connected to a remote fire alarm system.
Smoke alarms often experience false alarms as a result of smoke produced from cooking, smoking and other non-threatening situations. Thus, it is desirable to be able to temporarily disable or desensitize a smoke alarm under such false-alarm conditions.
For this purpose, many modern smoke alarms include what is referred to as a silencing feature or hush mode. Typically, smoke alarms include a test button to allow a user to initiate a self-test function to assure the smoke alarm is working properly. In order to simplify smoke alarm construction and operation, many manufacturers have incorporated the hush mode into the test button. As such, when the test button is depressed, the smoke alarm will go into a silent or decreased sensitivity mode for a predetermined period of time, after which the smoke alarm will rearm itself in its normal operating mode.
FIG. 1 shows a typical photoelectric smoke alarm chip 100, Model No. A5358CA or A5366CA manufactured by Allegro Microsystems, Inc., connected to external circuitry with which it would normally be used. The entire circuit is contained within a smoke alarm enclosure 102. A power source 104 is provided to provide VDD and VSS (ground) for the circuit and the chip 100.
The enclosure 102 is provided with a smoke chamber 106 in which a infrared emitting diode 108 and an infrared photo diode 110 are contained. The emitting diode 108 is connected between pin 6 of the chip 100 and VDD of the circuit. The emitting diode 108 is driven by a oscillator and timing circuit 112 provided on the chip 100. The detecting diode 110 is connected between pin 3 of the chip 100 and VDD of the circuit. The output of the detecting diode 110 is amplified by a photoelectric amplifier 114 provided on the chip 100. The output of the photo amp 114 is fed to a logic circuit 116 provided to the chip 100.
When smoke particles enter the smoke chamber 106, the particles cause the light emitted by the emitting diode 108 to be diffracted before it is received by the detecting diode 110. The logic circuit 116 of the chip 100 detects this diffraction and, when appropriate, causes a horn driver 118 provided on the chip 100 to drive an external horn 120 which generates and audible alarm.
A momentary push button 122 connected between VDD and pin 16 of the chip 100, when pressed, causes the chip 100 to test the smoke alarm circuit and drive the horn 120 if the circuit is functioning properly.
To avoid false alarms, a hush mode is provided to the chip 100. To utilize the hush mode, a voltage divider VD comprising two resistors R1, R2 is connected between the power source 104 and pin 4 of the chip 100. A ratio of the voltage provided by the voltage divider VD and VDD sets a decreased sensitivity level of the smoke alarm circuit when hush mode is active. Whenever the push-button 122 is pressed, hush mode is activated for a predetermined period of time. To disable the hush mode entirely, the voltage VD provided to pin 15 of the chip 100 must be set to VSS. In this way, the hush mode is either permanently enabled or permanently disabled, depending upon the circuit configuration.
In recent years, there has been a need to provide inexpensive centralized fire alarm systems. In order to do this, many manufacturers have taken inexpensive individual smoke alarms and linked them together to form a centralized system. One of the features of these systems is the ability to perform a self-test of all of the smoke alarms in the system simultaneously from a centralized or remote location.
However, when smoke alarms having the hush mode described above enabled are used in such a network system, the activation of a remote self-test will engage the hush mode. As a result, all of the smoke alarms will be silenced or have reduced sensitivity for a period of time. During this time period, the areas protected by the smoke alarms will be at an increased risk of an undetected fire hazard. Further, the occupants of the individual areas may not be aware of the reduced sensitivity of the smoke alarm. Thus, it would be desirable to provide a means for selectively disabling and enabling the hush mode of this type of smoke alarm.
To overcome the disadvantages of the prior described above, the present invention provides a circuit for disabling the hush mode of a smoke alarm during a remote test. According to an aspect of the present invention, a hush mode disabling device for a smoke alarm having a self-test function, a hush mode that engages upon activation of the self-test function to silence or desensitize the smoke alarm for a predetermined period of time, and a remote self-test controller is provided. An improvement comprises a hush mode disabler for determining whether the self-test function has presently been activated by the remote self-test controller and for disabling the hush mode only if the self-test function has presently been activated by the remote self-test controller.